I. Field of the Invention
The present invention relates generally to internal combustion engines, and more particularly, to an open chamber stratified charge internal combustion engine.
II. Description of the Prior Art
Stratified charge combustion is well known and quite old in the art of internal combustion engines. Theoretically speaking, any engine in which the fuel and air are not intimately mixed throughout the combustion space during the combustion time is defined as a stratified charge engine. In this broad, theoretical sense any type of compression engine is a stratified charge engine.
A more practical definition, and one now commonly accepted throughout the world, would include, as a stratified charge engine, all engines in which: (1) the mixture is not homogenous throughout the combustion space and (2) combustion is initiated by outside electrical means.
As such an engine can have either two totally different homogenous mixtures of different air/fuel ratios or a multiplicity of air/fuel ratios across its combustion space, and be called a stratified charge engine. Typical of the first of these are so-called divided chamber or precombustion chamber stratified charge engines, which normally employ two well defined combustion chambers. The second would include all so-called open chamber stratified charge engines.
Divided chamber stratified charge engines, dating back more than 60 years, have received considerable attention lately and have even been introduced commercially. These engines work with a rich, ignitable ratio in the small precombustion chamber and load dependent, variably lean ratios in the main combustion chamber. The main advantage of this system is that it lends itself well to outside controls to produce a reasonably clean exhaust. The control flexibility of the system allows it to be programmed to comply with the varying requirements of different testing cycles. The disadvantages of this system are: (1) low thermal efficiency; (2) the requirement for complicated and sensitive control mechanisms; and (3) the inability of such engines to yield both high economy and low exhaust emissions at the same time.
In general, open chamber stratified combustion engines are very closely linked to open chamber compression ignition engines enjoying many of their good characteristics while correcting or improving upon those which are unacceptable. Like open chamber diesels, the air intake is basically unthrottled for high volumetric efficiency and minimum pumping losses. Supercharging is easily accomplished since only air needs to be handled. Combustion is accomplished by electrical ignition of the injected fuel rather than by the high compression pressures and temperatures required by open chamber compression ignition engines to achieve auto-ignition of the fuel.
In open chamber stratified charge engines, the compression ratio can be adjusted for the optimum compromise between thermodynamic efficiency and friction, mechanical loads, manufacturing tolerances, etc., that is at approximately 11 to 13:1. Combustion proceeds smoothly, devoid of the high noise and firing pressures characteristic of open chamber diesel combustion.
Auto-ignition of the fuel, the heart and essence of compression ignition engines, remains, to this day, as the worst drawback of this type of engine. Long delays between the beginning of injection and the initiation of combustion result if the compression ratio is too low. To reduce the delay to produce quiet operation and high speed capabilities requires compression ratios over 20:1. Delay time is also a controlling factor in emissions of oxides of nitrogen. With long delay time there is uncontrollable burning and heat release of a large quantity of the fuel introduced during the delay period producing relatively high amounts of NO.sub.x as well as noise. Open chamber stratified charge engines, by initiating combustion through spark ignition, operate with controlled delay times and, therefore, produce smooth, noiseless ignition with minimum amounts of oxides of nitrogen.
The relatively long time delays typical of open chamber compression ignition engines have prevented these power plants from operating at the rotational speeds required by light duty automotive applications.
Open chamber, stratified charge engines exhibit the good nozzle related hydrocarbon emissions profile as previously explained, but with some designs in which the fuel makes excessive wall contact prior to combustion, hydrocarbon emissions are relatively high due to the wall quenching effects. In some cases, especially with fuels which may generate odoriferous compounds, exhaust odor can be very noticeable.
In summation the failure of most open chamber stratified charge engines has been the basically unconfined design of the chamber, reminiscent of an open pot in which air, fuel, and spark are thrown together with little but hope that combustion will take place as originally intended.